Detach not echoed back in multi-hop link route due to wrong session being closed

In a multi-hop link route involving 2 routers and a broker, the detaches fail to be forwarded by one router to another because of the wrong session being closed.

Steps to reproduce

To reproduce,
(1) start two routers with simple-topic-a.conf and simple-topic-b.conf (attached)
qdrouterd --conf simple-topic-a.conf
qdrouterd --conf simple-topic-b.conf
(2) start artemis broker on port 5673 with examples topic configure (e.g. see broker,xml attached)
(3) run two instances of the modified simple_recv example as attached (the change is that the client waits for the detach to be echoed back before exiting)
e.g.
python simple_recv_modified.py -m 10 &
python simple_recv_modified.py -m 10 &
(4) run simple_send.py example from proton python
e.g.
python simple_send.py -m 10

Sometimes only one of the receivers will exit. Sometimes both receivers dont exit. The receivers are waitingfor the detach frames to arrive from router A but they never do. If you enable PN_TRACE_FRM you can see that the detach is never received back from the router A.